Maximum Standard Length

H. auca appears very similar to the congener H. anisitsibut can be told apart by possessing a single maxillary tooth always with 5 cusps (vs. 3-5 cusps in H. anisitsi), dentary depth 40.7-47.6 % of dentary length (vs. 50.0-53.3 %), and possessing small hooks on the dorsal, caudal and pectoral fins in males (vs. lacking hooks on these fins in males).

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